Dave Dietzler
Basic Lunar Geology
It is believed that the Moon was once covered by a magma ocean several hundred kilometers deep. Heavier minerals like pyroxenes, olivine and chromite sank while lighter anorthositic material floated to form the upper crust. Volcanism and massive asteroid impacts shattered the crust and molten lava flowed to the surface to fill in the mare basins. While iron sank to the core chalcophile elements like copper and PGEs sank to the mantle. Central crater peaks and mass-cons may represent mantle or deep crustal up-thrusts or rebounds from these impacts. G.J. Taylor and Linda Martel believe that chromium, platinum group metals, nickel and titanium may be found in central peaks and crater rims[1]. They also think that silver, Pt-group, zinc, mercury, lead and copper could be found in pyroclastic deposits near volcanic vents in the maria. It is fairly certain that orange and green glass micro spheres discovered by Apollo missions were spewed out from volcanic vents, now long extinct, so deep lavas from the lower crust and upper mantle bearing valuable metals may have reached the surface or subsurface beneath the homogenized regolith. Even so, “ores” of silver, platinum and copper are likely to be very low grade, and novel extraction methods will be needed to recover these metals that are often called LDEs or lunar deficient elements.
Bioleaching
Bioleaching involves the use of micro-organisms to extract metals from low grade ores and has been performed successfully on Earth to obtain gold, copper and uranium[2]. About 20% of the world’s copper is produced by bioleaching. This type of process has been used to extract uranium from the Elliott Lake district in northern Ontario, Canada[3].
Bioleaching of nickel, zinc and cobalt can be done with thermophyllic bacteria but has not proven economical; however, on the Moon where resources are sparse and imports comparatively expensive, this may be worthwhile. Nickel and cobalt are used to alloy steel and zinc is used to alloy magnesium.
Thiobacillus ferrooxidans, Leptospirillum ferrooxidans, Thiobacillus thiooxidans, Sulfolobus species and others have been used for bioleaching. Acidiphilium, Sulfobacillus, Ferroplasma, Sulfolobus, Metallosphaera, and Acidianus have also been used. These bacteria tolerate acids and metabolize sulfur. Weak solutions of acids are dripped through the ore and a bacterial liquor forms that is then electrolytically or chemically processed[4]. Sometimes this requires water and organic substrate like potato peels as well as solvents to extract the metals from the bacterial mass. Chaff from crops may be used for bioleaching rather than livestock feed. Precious water will be recycled. If bioleaching becomes a major industrial activity on the Moon we will be pressed to conserve our vital water and hydrogen resources for this instead of wasting them in the form of rocket fuel. Only ores containing sulfur can be bioleached because the bacteria feed on sulfur. Bioleaching does not require lots of energy but it is slow. High temperature roasting and smelting is not required, so there are decided benefits in addition to the fact that bioleaching can get metals from low grade ores.
References
1)PROSPECTING FOR LUNAR AND MARTIAN RESOURCES. G. Jeffrey Taylor and Linda Martel
(Hawai`i Institute of Geophysics and Planetology, University of Hawai`i,
http://www.mines.edu/research/srr/2001abstracts/Taylor.PDF
2) MINING AND MINERAL FACT SHEETS http://www.fact-index.com/b/bi/bioleaching.html
3,4) BIOENGINEERING-MICROBIAL MINING http://www.bioteach.ubc.ca/Bioengineering/microbialmining/
MORE INFORMATION
http://www.imm.org.uk/gilbertsonpaper.htm
http://www.nrcan-rncan.gc.ca/biotechnology/english/m_bioleach.html
http://en.wikipedia.org/wiki/Bioleaching
